sump filter?

[ndntakeover]

what is a sump/sump filter?

and its use?

[ndntakeover]

ive heard it being used in saltwater tanks

[PostalPenguin]

Its basically a tank outside of the display tank that you put all the support equipment in like the skimmer, heater, etc. Its also a place for beneficial organisms to grow. In the main tank they would be eaten clean but the sump ensures that there is always more reproducing. You can also place macro-algae in it to keep algae from growing in your display tank.